[Xen-devel] Possible bug with huge unflushed console buffer

[Mark van Dijk <lists+xen@xxxxxxxxxxxxxx>]

Greetings list,

Yesterday the following scenario took place. In short, I had a HVM host
with a poorly configured firewall. It logged way more than it should,
and it had been doing that for days. IPTables entries with -j LOG
show up in the console. I told Konrad about this but I said it was a PV
host while in fact it is concerning a HVM host.

Anyway, when I saw that this was the case I corrected iptables and then
I removed those faulty log entries from the logfiles in /var/log.
Finally I issued /etc/init.d/rsyslogd reload.

Suddenly the server stopped responding at all, not even arp requests
were answered. I opened up a console via xl (none was open before
this) and I was greeted with a crazy amount of log entries - it took
about five or six minutes before the whole buffer was flushed to my
screen. Then the server responded again.

Today I viewed syslog's messages in detail and found this and a lot of
similar entries:

http://pastebin.com/Ga7aE7hb

So the questions that I have now are - Is this a bug? How is console
history handled and where is the console's unread history stored?
Somewhere in the hypervisor or in dom0 or domU memory space? Is there a
limit to how much info can be stored?

The behaviour I encountered i.e. a system lock seems to suggest that
there was some kind of buffer overflow. And this can be achieved by
something as simple as 'iptables -I INPUT -j LOG'. Perhaps it is a wise
idea to consider xl console -c to clear the console's history, then at
least I could exit the console and clear unsent messages...

I am not receiving xen-devel messages, so please CC me on replies.
Thank you.

-- 
Stay in touch,
Mark van Dijk.                  ,-----------------------------------
-------------------------------'           Wed Aug 08 15:29 UTC 2012
Today is Setting Orange, the 1st day of Bureaucracy in the YOLD 3178

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